1.Introduction about Network
and Network Security
Network :- A network is defined as a group of two or
more computer systems linked together.
Why Network ?
Computer networks allow the user to access remote programs and remote
databases either of the same organization or from other enterprises or public
sources. Computer networks provide communication possibilities faster than other
facilities. Because of these optimal information and communication possibilities,
computer networks may increase the organizational learning rate, which many
authors declare as the only fundamental advantage in competition.
Types Of Network
 local-area networks (LANs): The computers are geographically
close together (that is, in the same building).
 wide-area networks (WANs): The computers are farther apart
and are connected by telephone lines or radio waves.
 campus-area networks (CANs): The computers are within a
limited geographic area, such as a campus or military base.

 metropolitan-area networks MANs): A data network designed
for a town or city.
 home-area networks (HANs): A network contained within a
user's home that connects a person's digital devices.
Network Characteristics
In addition to these types, the following characteristics are also used to categorize
different types of networks:
 topology : The geometric arrangement of a computer system. Common
topologies include a bus, star, and ring..
 protocol : The protocol defines a common set of rules and signals that
computers on the network use to communicate. One of the most popular
protocols for LANs is called Ethernet. Another popular LAN protocol
for PCs is the IBM token-ring network .
 architecture : Networks can be broadly classified as using either a peer-topeer or client/server architecture.
Computers on a network are sometimes called nodes. Computers
and devices that allocate resources for a network are called servers.
Computer Security
The meaning of the term computer security has evolved in recent years. Before
the problem of data security became widely publicized in the media, most people‟s
idea of computer security focused on the physical machine. Traditionally,
computer facilities have been physically protected for three reasons:
 To prevent theft of or damage to the hardware
 To prevent theft of or damage to the information
 To prevent disruption of service
Strict procedures for access to the machine room are used by most
organizations, and these procedures are often an organization‟s only obvious
computer security measures. Today, however, with pervasive remote terminal
access, communications, and networking, physical measures rarely provide
meaningful protection for either the information or the service; only the
hardware is secure. Nonetheless, most computer facilities continue to protect
their physical machine far better than they do their data, even when the value
of the data is several times greater than the value of the hardware.